This invention relates to coating, impregnating, and adhesive compositions of a resin-forming polyepoxide mixed with a polyfunctional compound containing cyclic oxazolidinyl groups.
Polyepoxides, such as, for example, those obtained by reacting epichlorohydrin with polyhydric phenols in the presence of caustic, are promising materials for use in many industrial applications as they can be reacted with curing agents to form insoluble infusible products having good chemical resistance. The conventional polyepoxide-curing agent systmes, however, have a drawback that greatly limits the industrial use of the polyepoxides. The known mixtures comprising the polyepoxide and curing agent set up rather rapidly, and this is true even though the mixtures are stored in air-tight containers away from moisture and air and even though the temperature is maintained quite low. This difficulty necessitates a mixing of the components just before use and a rapid use of the material before cure sets in. Such a procedure places a considerable burden on the individual operators, and in many cases, gives inferior products resulting from inefficient mixing and too rapid operations.
Numerous attempts have been made to provide a latent curing agent for polyepoxides, by which is meant the type of resin-forming organic compound containing a plurality of vic-epoxy groups of the formula ##STR1##
Such compounds may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic, or heterocyclic and may be substituted, if desired, with substituents such as chlorine atoms, hydroxyl groups, ether radicals, and the like.
Holm, U.S. Pat. No. 3,291,775 and Gardner and Keough, U.S. Pat. No. 3,547,886 disclose the use of certain polyimines obtainable by reacting a ketone or aldehyde with a polyamine to cure or resinify a polyepoxide.
Hankins and Emmons, U.S. Pat. No. 3,037,006, disclose that copolymers of 5 to 25% by weight of an N-(acryloxyalkyl)-oxazolidine or an N-(acryloxyalkyl)-tetrahydro-1,3-oxazine embraced by the formula ##STR2## where
n is an integer having a value of 1 to 2,
m is an integer having a value of 2 to 3,
R.sup.1, when not directly joined to R.sup.2, is selected from the group consisting of hydrogen, phenyl, benzyl, and C.sub.1 -C.sub.12 alkyl groups,
R.sup.2, when not directly joined to R.sup.1, is selected from the group consisting of hydrogen and C.sub.1 -C.sub.4 alkyl groups and
R.sup.1 and R.sup.2, when directly joined together, form a 5- to 6-carbon ring with the attached carbon atom of the ring in the formula, i.e., R.sup.1 and R.sup.2, when joined together, are selected from the group consisting of pentamethylene and tetramethylene,
can be mixed with polyepoxides for the production of insoluble and infusible crosslinked coatings. There is no suggestion in this patent that the copolymers in which R.sup.1 and R.sup.2 are independent saturated hydrocarbon groups or together an alkylene group forming a 5- to 6-carbon ring with the attached carbon of the ring in the formula would provide distinctive and unexpected storage-stability properties that are lacking in those copolymers in which either or both R.sup.1 and R.sup.2 is, or are, hydrogen atoms. R.sup.1 and R.sup.2 are attached to the 2-position carbon in the heterocyclic ring of the formula.